1. Field of the Invention
The present invention relates to a cleaning device, a liquid application device and an image forming apparatus, and more particularly to cleaning technology for a conveyance device which holds and conveys a medium.
2. Description of the Related Art
With the object of forming good images in a cut sheet printing system of a general printing machine in which image formation is carried out using an inkjet method, there is a process of applying an aggregating reaction liquid (hereinafter referred to as a “treatment liquid”) using roller application in a stage before image formation using ink, thereby forming an inkjet receiving layer on standard printing paper. In an image forming process based on an inkjet recording method, it is desirable to use a roller application method for applying the treatment liquid in order to form a thin layer of treatment liquid having low viscosity over the whole surface of a recording medium.
FIG. 25 is an illustrative diagram showing a schematic view of a treatment liquid application process which employs a roller application method using an application roller. As shown in FIG. 25, in order to form a borderless image over the whole surface of a recording medium 604 held on a conveyance drum surface (circumferential surface) 600A of a conveyance drum 600, it is necessary to apply treatment liquid over a region broader than a region where the image is formed, and therefore the width of the application roller 606, which applies the treatment liquid, is greater than the width of the recording medium 604. The region defined with dashed lines in FIG. 25 is the region where the treatment liquid is applied on the conveyance drum surface 600A, and here the treatment liquid is applied to the outside of the recording medium 604.
The treatment liquid having been excessively applied (hereinafter referred to as “excess treatment liquid”) accumulates as the printing continues, and when the accumulated amount of the excess treatment liquid becomes greater than the amount that can be held on the conveyance drum surface 600A, the excess treatment liquid starts to trickle down the conveyance drum surface 600A. If the excess treatment liquid trickling down the conveyance drum surface 600A (hereinafter referred to as “trickling excess treatment liquid”) adheres to the successively conveyed recording media, then this leads to decline in print quality. Furthermore, if the trickling excess treatment liquid adheres to the conveyance mechanism, such as grippers, which grip the leading end portion of the recording medium 604, then this not only gives rise to conveyance abnormalities of the recording medium, such as jams, but also causes problems such as corrosion of the conveyance drum itself and the peripheral members of the conveyance drum, such as the jacket, grippers, and the like, due to adherence of the strongly acidic treatment liquid. Therefore, it is necessary to remove the excess treatment liquid rapidly. One method proposed for removing soiling and ink adhering to a blanket drum and an ink drum of a printing machine is a method which employs a so-called cleaning cloth (web).
Japanese Patent Application Publication No. 06-143545 discloses a cylinder cleaning device composed in such a manner that the outer circumferential surface of a cylinder is cleaned by pressing a cleaning cloth that relatively moves against the outer circumferential surface of the cylinder (drum). The cylinder cleaning device is composed in such a manner that the cleaning cloth is pressed with a pad having a circular arc shape, the circular arc portion of the pad is advanced and retracted with respect to the cylinder by altering the length of the chord subtending the arc of the pad, and the cleaning cloth is thereby pressed reliably against the drum.
Japanese Patent Application Publication No. 11-070641 discloses a cleaning device for a print drum which sprays a cleaning liquid toward a pressure drum from a plurality of nozzles disposed along the axial direction of the pressure drum (print drum) and cleans the pressure drum by pressing a cleaning cloth by means of an incorporated blade.
Although the methods for wiping away soiling by pressing the cleaning cloth against the pressure drum described in Japanese Patent Application Publication Nos. 06-143545 and 11-070641 effective in wiping away ink residue, and the like, the methods are not suitable for wiping away treatment liquid that has been applied thinly over a broad area, in terms of the capacity for absorbing liquid. More specifically, the cleaning cloth becomes saturated with the liquid immediately after the start of wiping, the cleaning cloth that has reached liquid saturation displays a massive decline in cleaning properties, and it becomes difficult to remove the liquid effectively. If using the cleaning liquid, the amount of liquid to be absorbed increases yet further, and then the removal of the treatment liquid and the cleaning liquid becomes even more difficult. In addition to this, there is also a problem in that by continuing to press the cleaning cloth that has been saturated with the liquid against the pressure drum, the liquid is caused to bleed out from the cleaning cloth and the bleeding liquid adheres again to the surface of the pressure drum.
One possible response to the above-described problems might be to wind up the portion of the cleaning cloth that has been saturated with the liquid, at a short repetition cycle (almost continuously), in such a manner that the surface is abutted with and wiped with dry cloth at all times, but since this solution consumes a very large amount of cleaning cloth, it becomes necessary to replace the cleaning cloth with great frequency, as well as being necessary to rotate the pressure drum a number of times in order to achieve sufficient cleaning. In any case, the cleaning process takes a long time, thus leading to poor efficiency.
On the other hand, another possible response might be to employ a material having a greater liquid absorption volume than the cleaning cloth (for example, a sponge sheet, sponge roller, or the like) as a wiping member. However, although sufficient liquid absorption capability is displayed for a certain period of time from the start of wiping, the wiping member reaches liquid saturation as wiping progresses, and if the wiping of the cleaning liquid is carried out over a long period of time, the problem of liquid saturation ultimately occurs similarly to when using the cleaning cloth. More specifically, even if a wiping member having a greater liquid absorption volume than the cleaning cloth is used, it becomes necessary either to frequently replace the wiping member, or to provide a separate mechanism (a vacuum sucking device, a squeezing roller, or the like) for collecting the liquid that has been absorbed by the wiping member.
As a further cleaning method, Japanese Patent Application Publication No. 10-095104 discloses a roller cleaning device for a rotary printing machine, which is composed in such a manner that cleaning is carried out while applying cleaning liquid to the circumferential surface of a swing roller, in such a manner that the cleaning liquid used for the cleaning is collected by a blade of which the edge is abutted on the circumferential surface of the swing roller.
However, removing the liquid by means of a doctor blade as described in Japanese Patent Application Publication No. 10-095104 is not suitable for a liquid that has low viscosity and is applied in an extremely thin coating of about several micrometers (μm), compared to a liquid having a certain viscosity or a liquid that has been partly cured (for example, ink soiling). In other words, the liquid passes through the clearance between the edge of the doctor blade and the pressure drum and it is difficult to remove sufficiently the liquid adhering to the pressure drum.
Furthermore, it is also possible to use a wiper blade, instead of the doctor blade. FIG. 26A is a conceptual diagram showing a schematic view of a wiping process by a doctor blade, and FIG. 26B is a conceptual diagram showing a schematic view of a wiping process by a wiper blade.
As shown in FIG. 26A, the wiping process in which a blade 622 is brought to proximity with a wiped surface 620 while being inclined against the movement direction of the wiped surface 620 (indicated with the arrowed line) is referred to as a “wiping process using a doctor blade”. On the other hand, as shown in FIG. 26B, a wiping process in which the blade 622 is brought to proximity with the wiped surface 620 while being inclined along the movement direction of the wiped surface 620 (indicated with the arrowed line) is referred to as a “wiping process using a wiper blade”.
In either case where the blade 622 is used as the doctor blade or the wiper blade, the liquid slides down the working face on the upstream side of the blade 622 in terms of the movement direction of the wiped surface 620. A wiping process using the wiper blade is desirable for removing (wiping) the liquid that has relatively low viscosity and has been applied thinly over a broad range.
In the conveyance drum 600 employed in the drum conveyance method shown in FIG. 25, a holding member (gripper) 608, which holds the leading end portion of the recording medium 604, is arranged and the holding member 608 has a structure of which a portion projects beyond the conveyance drum surface 600A. Therefore, in order to avoid collisions between the holding member 608 and the application roller 606 and the blade (not shown) for cleaning the conveyance drum surface 600A which are disposed adjacently to the conveyance drum surface 600A, it is necessary to separate the application roller 606 and the blade from the conveyance drum surface 600A when the holding member 608 passes.
On the other hand, when the blade is withdrawn from the conveyance drum surface 600A, the portion of liquid (liquid pool) that has been wiped by the blade immediately beforehand is left at a position on the conveyance drum surface 600A that passes by the wiping region of the blade while the blade that is disposed adjacently to the holding member 608 is being withdrawn. The liquid accumulates in the liquid pool while the cleaning of the conveyance drum surface 600A is repeated, and there is a problem in that eventually, trickling of the liquid occurs.